Art of separating suspended particles from gaseous bodies.



o. 895,729. PATENTED AUG. 11, 1908. P. G. GOTTRELL.

ART OF SEPARATING SUSPENDED PARTICLES FROM GASEOUS BODIES.

APPLICATION FILED JULY 9,1907.

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g I C c. l T i I WIT/{E5959 lA/VE/W'fifl W BY fir-XM I A7TUHNEY PATENTED AUG. 11, 1908.

I F. G. COTTRELL. I ART OF SEPARATING SUSPENDED PARTICLES FROM GASEOUS BODIES.

APPLICATION FILED JULY 9,1907.

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PATENT OFFICE.

FREDERICK GARDNER COTTRELL, OF BERKELEY, CALIFORNIA, ASSIGNOR TO INTER- NATIONAL PRECIPITATION COMPANY, RATION OF CALIFORNIA. 1

OF SAN FRANCISCO, CALIFORNIA, A CORPO- ART o'r sEPAiaa'rmG. SKUSPENDED PARTICLES FROM. GABEOUB Bonnets,

Specification of Letters Patent.

Patented Aug. 11,1908.

Application filed July 9, 1907. Serial No. 882,923.

T 0 all whom it may concern; Be it known that I, FREDERICK GARDNER COTTRELL, a citizen of the United States, residin at Berkeley, in the county of Alameda tate of California, have invented certain new and useful Improvements in the Art of Se arating Suspended Particles from Gaseous fiodies, of which the. following is a specification.

My invention relates to the art of separatin finely divided ui s, originally he in suspension in bodies of gas ,or vapor, by the application of electric charges.

It has long been known that when gases containing suspended particles, such as smoke, fo dust, mists, etc. ,are brought into the neigh orhood of a body charged to as high electric potential with respect to its surroundings, that is, into an electric field, the suspended matter tends to be deposited. This is especially noticeable in the case of charged points; the particles bein repelled .from these. It has, repeatedly, een proposed to em loy these agencies in technical operations; ut, difficulties in their application and control have, up to the present, greatly limited their general introduction on a practical scale.

The utility and economic importance of an efiicient'process of this character may readily be appreciated by reference to. such matters as; the efforts now being made to clean iron blast-furnace gas, of dust, preparatory to its use in gas engines; the extensive fume and dust fiues, bag houses, and the like, employed in the lead and copper smeltersyand the filtering systems to remove mist in the sulfuric acid plants, to say nothing of the problem of destroyin fo and mists in the open .air, both on lan anc water.

' The im rovements herein described are the logica outcome of an analysis of the underlying rinciples, with dueregard to the 'structuraFand-1nstrumental difficulties to be met with in their application. The result of such analysis leads. to the following as conditions favorable for successful operation:

First, the use of essentially direct currents, that is, constancy of direction of the force in the electric field. The terms essentially direct, and, essentially constant polarity are, herein, throughout, to be understood as including, if necessary, conditions involving 1particles of solids or liqcompared with, the time necessary for the deposition of 'the individual pended matter.

Second, the char ing of su, ended particlesby the action 0 an electro e presenting a considerable exteht of surface over which a fairly uniform and .moderately intense discharge of the brush or glow type, is maintained into the surroundln gas.

Third, the attraction and collection of the particles thus charged, by electrode surfaces of op osite polarity upon which brush or glow ischarge is reduced to a minimum.

Fourth, the passage of the 1particle-laden gases through the electric fieh produced by these electrodes, in such wise as to secure the most thorough and uniform treatment of the whole.'

Fifth, aside from the current carried by the gas and moving particles, the maintenance of as perfect insu two electrodes, more es ecially guarding against short circuits and oaks through the material deposited out of the gases themselves during the operation. It must be particles of susation as possible between the...

further borne in mind that any process which in itself is tomaterially advance the state of aving easily rep aceelectrical potentials of two types of electrode surface. Second. The charging of suspended particles by brush or glow dlscharge from the one type of electrode surface. Third. ,The attraction of the thus charged particles to the other type of, electrode surface. Fourth. The the sus ende particles upon the surface of the soli insulating supports between the two types of electrodes.

- As so man of the failures of previous processes in this ine appear'to have resulted from the impracticabillty of meeting the demands of delicate ad i'ust- I little attention, and

prevention of the deposition of of these requirements with suitable economic with shar apparatus, I have in the following descript1on of m own improvementsindicated how each of t 1e chief requirements ma actually be met in practice. This is facitated by reference to the accompanying drawings in which Figure 1 is a eneral view of an apparatus, diagrammatically illustrated, 'by means of which my iin rovements may be carried out. Fig. 2 is a iagrammatic view, showing a modification of the electrodes. Fig.3 is a view showing another modified arrangement of the electrodes. Fig. 4 is a view showin a modification of the synchronous contact evlce.

Referring to Fig. 1, the gases or vapors containing the sus ended particles enter the precipitation cham er A through the pipe B, and come into the proximit of the active electrode C,"the body of whi'c may be made of any suitable material./\ 'In the apparatus shown, the second active electrode, (the two oppositely char ed conductors or systems of conductors, between which the preci itation actuall takes lace will hereafter P y P 7 be referred to as the active electrodes whatever their structure or other relations may be) conslsts of the walls of the precipitation chamber itself; but, the apparatus is not necessarily limited to this form of construction. For instance, in dispelling fog, the ground or water might be made one electrode and the other suspended freely above it. If the surface both electrodes is as smooth as possible, t e efficienc of the a paratus becomes relatively smal but, if t e surface of one of the electrodes. is supplied points and the potential dlfl'erence is hi enough, a rapid repulsion of the particles from these ma be observed, together with a correspondlng collection of deosited material on the other electrode. Fiodern theories eicplain this action on the ground that the gas in the neighborhood of the points becomes ionized, chiefly by brush or glow discharge, and the ions combine with or condense upon the suspended articles, dragging these with them toward odies of opposite olarity. If, in each considerable re ion of the gas, wholly or partially bounde by the electrodes of opposite polarity, there are points on but one of the active electrodes, the ionization of the as, roduced in this region, will be practical y of ut one sign, and the particles will all move toward the other I electrode, provided the polarity of the elec;

trodes remains the same. If, on the other hand, both electrodes bounding this region are provided with points, or their polarity is being rapidly reversed, ions of both signs will be produced in the gas space and attach themselves to particles. Some of these will reach each electrode, but others will mutually neutralize each other in the gas space,

possibly giving rise to larger aggregates m so doing, but, on the whole, the efficiency of recipitation is reduced; This is particuarly true when the electrodes are excited from a source of alternating current, as in this case the same particle is drawn first one way and then the .other, if the-duration of alternation is small compared with the time faces is of the utmost importance. Bare metallic electrodesof various forms and strue: ture, includin rods or wlre with shar po1nts, wire gauze, airly fine wire brlst es, thin sheets, disks, etc.. have all beentried and found impractical for treating large masses of gas; the chief objection to them lying in the intensity of electric field required and the great tendency for the dischar e to become sharply localized. These difficulties are all avoided and the Ci'llGlOIlCY and ease of adjustment of the apparatus reatly increased, if the electrodes are simply covered,

in whole or in part, with some soft, fibrous material, such as cotton or asbestos, resenting' a pubescent surface. These, a though relatively poor conductors,-. amply suffice. under the usual conditions, and, if necessary, the material may be so treated as to increase its conductivity. Such an electrode shows in a dark room a uniform development of luminous discharge all over its surface, even when at a comparatively great distance from the other electrode. This permits a much lower potential difference, and the employment of a greater and less uniform distance between the electrodes.

The form of active electrode 0, in Fig. 1, has been found very satisfactory. It consists of a cage of wire suppofted by a conducting rod D. Upon the surface of the cage, including the bottom, is wound or stretched some asbestos, very conveniently in the form of a small cord or thread a. The as, issuing from the inlet B, receives the disc arge from the filaments c of asbestos on the bottom of the cage, and many of the particles are driven back and precipitated in the lower art of the chamber. Those that escape an( pass between the asbestos and wire meshes into the interior of the cage, are found to follow, approximately, the direction of the arrows,

emerging from the sides of the cage, appar- Owing duced somewhat by bringing the connection to and support for the inner electrode through the outer wall of the precipitation chamber in a part where the gas has its maximum purity from suspended matter.. To

further guard against any contamination from suspended matter that may have escaped precipitation by the electrodes before I reaching this part of the chamber, an arrangefrom the precipitation chamber A,

ment is shown in Fig. l for passing in about the insulatingsupport E ofthe inner electrode, a slow current of pure dry gas through the inlet G. This is supposed to be supplied at a sullicient rate to prevent any diffusion or convection of the gas in the main chamber back into the constricted space ll, the walls of which may also be made of insulating material. Another method, which may be used as an alternative or as an auxiliary to that just described, consists in heating the space ll to such a temperature that deposition of the suspended matter, either in solid or liquid form, is impossible. In the drawing, the heating. is shown as ell'ected by a winding of wire It, through which an electric current is )assed; but, any other suitable means of heating may be employed.

'lhe deposited matter may be removed manner most convenient, the mode depending upon its character and amount. .f liq hid, it may be drained off from the bottom of the chamber. .lf 'solid, it'might be flushed down and out with liquid, or scraped out as a solid. These processes might be intermittent or continuous.

. presents installation an As previously stated, a direct current has decided advantages as a charging source for the electrodes, but its production by the usual means, at the potentials here desired,

certain well known technical difiiculties. For the current of the re atively small magnitude actually demanded by the present improvement, the method illustrated in Fig. 1 has answered well, and has the reat advantage of extreme sim licity, coup ed with ease of maintenance of the apparatus required. One of the active electrodes is permanently connected with one terminal of a high potential alternating current circuit, while the other active electrode is connected with the other terminal of the same circuit through a make-and-break, operated in synchronism with the alternations of the in any production of an electriccircuit, and in which contact is made once each cycle, and only for a portion of each cycle. By properly choosing the points in, the cycle at which the contact is madeanda broken, any difference of potential may bet impressed on the electrodes, from zero u to i the maximum of the alternating current me. F without having to alter the latter at all. is probable that in actual practice, the maxi mum will generally be chosen. p

In order to maintain the potential (,llfi ence of the active electrodes nearly at it maximum during the portion of each cycle when the connection with the alternating current line is broken, the condenser I may be connected in parallel with the active ole--- trodes, thus increasing the capacity of the electrode system as a whole, of which it is to be considered a art. The electrodes, in themselves, constitute an air or gas condenser, and in some cases may sullice without the auxiliary condenser l; and in any case, they supplement its capacity.

A very satisfactory device for the makeand-break above referred to has been found in a system of metallic contact points J, mounted on an insulating disk or hub K, driven by a synchronous motor L, run by the same system of altcrnating'current as that supplying the active electrodes, and by its rotation making and breaking contact between the brushes M-and N. The arrangement of the disk and contacts shown in Fig.

-l, assumes two com lete cycles for each revolution of the dis but, by a proper change in the number and position of the contact points and brushes, it may be adapted to any other whole number of cycles per revolution, and, if more convenient, the disk and contacts may be mounted directly upon or driven directly. from the shaft of the alternating current generator itself which supplies the system. The synchronous motor, or the generator, as the case may be, will, in practice, most probably be operated at a lower yoltagethan that used for charging the active electrodes, this being indicated by the introduction of the transformer 0 between these two circuits.

The above description serves to illustrate one of the simplest modes of carrying out my improvements. I shall now point out some of the modifications of detail which also fall within the scope of said improvements.

It is possible to combine smooth with pubescent surfaces on the same electrode and retain the advantage sought, if the disposition of the smooth and pubescent areas on the two electrodes of opposite sign be .such that nowhere are pubescent surfaces of opposite sign both discharging into the same region of gas. Fig. 2 serves to illustrate What is here meant. A is a flue through which the gas is'passing, and B B B B is an electrode,

-.,-ticles are being charged negatively, W ile' in each of the regions I) b, they are being charged positively, out, in no single region of any important extent are they receiv ng noteworthy charges of both slgns.

The relative motion between gas and electrode may, in some cases be best produced by moving'the electrode ltselfthrough the gas, as, for example when treat1ngra1r1n the open, or any gas In Very large chambers. Such terms as causing gas to pass through or past an electrode are to be understood as including such procedure. A further extension of the same plrmciple of electrodes shown in Fig. 1, is s own in the modified arrangement in Fig. 3. Herein is illustrated {the surrounding o the active electrode C of Fig. 1, by a concentric cylinder A of wire gauze or other suitable material, restingon the bottom of the main vessel A, and fornung an extension of the inner surface of this vessel. Surrounding this again is another concentric cylinder of slmilar construction forming a part of the electrode 0. The u per ortion of the electrode 0 may be ma e solid? if desired, to still further gu de the gas through the meshes of the several cylindrical shells. The principles of construction illustrated in Fig. 2 may, of course, also becombined with those of Fig. 3; and the number of concentric shells may be indefinitely increased. Both active electrodes may be 40 connected and disconnected twice each cycle to the two terminals of the alternatin cur rent circuit in such wise that their re ative polarity remains the same. This has the advantage of utilizing both alternations of each cycle. For this purpose, the disk, brushes and connections may be modified in some such way as is shown in Fig. 4. Corresponding parts are lettered as in Fig. 1. A second system of contact points J, similar ub K, its contact arcs between those of points systems of points J and J being insulated from each other by hub K. The brush N makes ermanent contact with oints J; and

brush l with points J. Brus es M and M each make contact intermittentlywith points J andiJC,

Having thus described my invention, what .0 I. claim as new and desire to secure by Lette'rs Patent is,

"' The improvement in the art of separat ln'gisuspended particles from gaseous bodies,

'w ch consists in subjecting said gaseous Cl bodies to the action of a system of electrodes points ividing the J in halves; the

to points J, is mounted on the o posite side of seems potent al by intermittent connection with a source of alternating current, at intervals synchronised With the period of said current. 2. The impro'tement in the art of separat- 1ng suspended particles from gaseous bodies, which consists in subjecting said particles to the act1on of the electrode surface. 3. The improvement in the art of separatmg suspended particles from gaseous bodies, which consists in subjectin the particleladen gases to the action of an essentially smooth and a pubescent electrode surface of widely different electrical potential.

4. The improvement in the art of separating suspended particles from gaseous bodies, which consists in subjecting the particleladen gases to the simultaneous action of an essentially smooth and a pubescent electrode surface of opposite and essentially constant olarity.

5. he improvement in the art of separat- 1ng suspen' ed particles from gaseous bodies, WhlOh. consists in causing the particle-laden gases to pass through ervious pubescent electrode surfaces, for t e purpose of imparting a charge to said particles.

'6. The improvement in the art of separating suspended particles from gaseous bodies, which consists in causing the particle-laden maintaine' dfat a high difference of electrical discharge from a pubescent gases to pass through a succession of pervious electrode surfaces alternately essentially smooth and of a posite olarity.

7. T e improvement in the art of separating suspended particles from gaseous bodies, which consists in causing the particle-laden pubescent and ternately opgases to pass through a succession of pervious electrode surfaces alternately ubescent' and essentially smooth and of a tcrnately opposite and essentially constant polarity.

8. The improvement in the art of separating suspended particles from gaseous bodies, which consists in maintaining the insulation between the active electrodes over the surface of the solid insulating supports, by supplying a current of clean gas to said surface.

9 he improvement in the art of separatinlg suspended particles from gaseous bodies, W ich consists in maintaining the insulation between the active electrodes over the surface of the solid insulating supports, by supplying a current of clean gas to said surface, apd supplementing the same by the heating 0 a perature to prevent the deposition of any conducting solid or liquid film.

10. The improvement in the art of separating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentially smooth and a pubescent electrode surface of opposite polarity, maintained at a high difference of electrical potential by intermittent connectionwi'ith a source of alternating current at intervals synchronized with the period of said alternating current.

11. The improvement in the art of separating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentiall smooth and a pubescent electrode surface of opposite polarity, maintained at a high differencc of electrical potential by large electrical capacity of the electrode system which undergoes intermittentconnection with asource of alternating current at intervals synchronized with the period of said alternating current.

1.2. The im )rovement in the art of separating suspendei particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentiall smooth and a pubescent electrode surface 0 opposite polarity, maintained at a high difference of electrical potential by intermittent connection with a source of alternating current at intervals synchronized with the period of said alternating current, and supplying a current of clean gas to the surface of the solid insulating supports between the active electrodes, for the purpose set forth. 13. The improvement in the art of separating suspended particles from gaseous bodies,

which consists in subjecting said gaseous bodies to the action of an'essentiall smooth and a pubescent electrodesurface o opposite polarity, maintained at a high difference of electrical potential by large electrical capac ity of the electrode system. which undergoes intermittent connection with a source of alternating current at intervals synchronized and S11 p with the period of said alternating current, and supplying a current of clean gas to the surface of the solid insulating supports between the active electrodes, for the purpose set forth.

14. The im )rovement in the art of separating suspende particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentially smooth and a pubescent electrode surface. of opposite polarity, maintained at a high difference of electrical potential by intermittent connection with a source of alternating current at intervals synchronized with the period of said alternating current; sup )lying a current of clean gas to the surface 0 the solid insulating sup orts between the active electrodes; Tementing the same by heating a zone 0 saidsurface to a sufficient temperature to prevent the deposition of any conducting solid or liquid film, for the purpose described. v

15. The improvement in the art of separating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentially smooth and a pubescent electrode surface of opposite polarity, maintained at a high difference of electrical potential by large electrical capacity of the electrode system which undergoes intermittent connection with a source of alternating current at intervals synchronized with the period of said alternating current; sup lying a current of clean gas to the surface of t 1e solid insulating supports between the active electrodes; and, supplementing the same byheating a zone of said surface to a SllfllClGIlt temperature to prevent the deposition of any conducting solid or liquid film, for the purpose described.

16. The improvement in the art of sepa- '.rating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentially smooth and a pubescent electrode surface of opposite and essentially constant polarity, maintained at a high difference of electrical potential by intermittent connection with a source of alternating current at intervals syncurrent.

17. The improvement in the art of separating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentially smooth and a pubescent electrode surface of opposite and essentiall constant polarity, maintained at a high difference of electrical potential by large electrical capacity of the electrode system which undergoes intermittent connection with 'a source of alternating current at intervals synchronized with theperiod of said alternating current.

rating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the action of an essentially smooth and a pubescent electrode surface of opposite and essentially constant polarity, maintained at a high difference of electrical potential by large electrical capacity of the electrode system which undergoes intermittent connection with a source of alternating current at intervals synchronized with the period of said alternating current, and supplying a current of clean gas to the surface of the solid insulating supports between the active electrodes, for the purpose set forth,

19. The improvement in the art of separating suspended particles from gaseous bodies, which consists in subjecting said gaseous bodies to the \action of an essentially smooth and a pubescent electrode surface of opposite and essentiall constant polar ty, maintained at a highdiflerence of electrical potential by intermittent connection with a source of alternating current at intervals synchronized with the period of said alternating current; supplying a current of clean gas to the surface of the solid insulating su ports between the active electrodes; an supplementing the same by heating a zone of said surface to a sufficient temperature to 18. The improvement in the art of sepaprevent the de osition of any conducting smooth and a pubescent electrode surface of opposite and essentiall constant polarity, maintained at a high difference of electrical potential by large electrical capacity of the electrode system which undergoes intermit- [tent connection with a source of alternating current at intervals synchronized with the period of said alternating current; supplying seams a current of clean gas to the surface of the 15 solid insulatin supports between the active electrodes; ans supplementing the same by heating a zone of said surface to a sullicient tern erature to )reventthede ositionof'any com ucting solid'orliquidlilm, or thcpurpose 20 described.

in testimony whereol' l have signed my name to this specification in the presence of two subscribing witnesses.

FREDERICK GARDNER CUT'lltllhb. Witnesses:

N. A. ACKER, 1). B. RionAiws. 

